Gen 3 Night Vision Goggles

An image intensifier tube is a vacuum electronic device that intensifies a weak visible light image to make it a bright visible image. An image converter is a vacuum electronic device that converts an invisible light image into a visible image. In an image intensifier tube and an image converter, when an external radiation image is formed on the photocathode, the photocathode emits electrons, which are accelerated or focused and accelerated by an electron lens, and then bombard the fluorescent screen to produce a brighter visible image.

The brightness gain of a single-stage image intensifier tube is usually between 50 and 100 times. Using fiber optic panels as input and output windows, image intensifier tubes can be cascaded. A three-stage cascaded image intensifier tube can obtain a brightness gain of 10 to 10 times. The cascaded image intensifier tube becomes a night observation instrument after being equipped with an objective lens, an eyepiece and a power supply. It can be used for military, astronomy, medicine, special photography, animal night habit observation, night surveillance, etc. This cascaded image intensifier tube is called the first generation of micro-light tubes, which are large in size and have poor anti-glare ability. Adding a microchannel plate to the electrostatic focusing or close-focusing system can make the single tube reach a brightness gain of 10 times, and it becomes a second generation image intensifier tube. The microchannel plate is actually a secondary emission current amplifier. It is an array composed of hundreds of thousands to millions of hollow glass fibers, each of which has a certain conductivity and a secondary emission coefficient greater than 1. Electrodes are coated on both ends of the microchannel plate, and a voltage of 600 to 1000 volts can be applied. After the photoelectrons enter the microchannel plate, the current is amplified by 1000 to 3000 times through the multiplication effect. The output electrons are accelerated and bombard the fluorescent screen, showing a visible light image.

In 1934, G. Holst and others made the first infrared image converter. When working, a high voltage is applied between the flat cathode and the flat fluorescent screen, and the cathode and the fluorescent screen are very close. This is a close focus system. After that, electrostatic focusing and electromagnetic focusing imaging systems appeared.